Solid Bridge Formation Between Spray-Dried Sodium Carbonate Particles

Abstract

Moisture migration caking of pharmaceutical excipients in the absence of load is a significant quality and stability issue. This study uses Atomic Force Microscopy (AFM) to examine a solid bridge formed between two 20 µm spray-dried sodium carbonate particles. The bridge is grown by repeatedly exposing the system to 70% RH and 30% RH cycles at 25°C. A comparison is made with the idealized bridge model developed by Tanaka (1978), which was previously verified using crystalline systems. The resulting system was found to be more complex and grew in two stages. The first stage consisted of linear growth to five cycles, followed by a more gradual expansion and the appearance of crystalline structures.

Keywords:

• Atomic Force Microscopy (AFM)
• Caking
• Sodium carbonate
• Spray-drying